Electrostatic filters are used, among other places, in garbage-incinerating facilities, power plants, or in industry in fired production plants, such as for cement, lime, gypsum, iron, or steel manufacturing, in order to filter solid particles that are difficult to separate, e.g., fine dust particles, from a flow of air, flue gas, or, in general, a gas. For this purpose, the gas flow is led through an electric field, in which electrons released by electrodes attach to the dust particles, travel together with the dust particles in the direction of collecting electrodes, where they are separated.
So that an electrostatic filter can clean the gas with the greatest possible efficiency, it must flow into or through the filter as uniformly as possible. A non-optimal flow into the filter leads to a nonuniform distribution of the dust, the temperature, or the flow rate in the gas flow, which results in reduced filtration efficiency and thus nonoptimal cleaning effect. Due to this nonuniform flow distribution, particle deposits can form very easily, which slowly reduce the cross section of the flow in the electrostatic filter and decrease its efficiency.
Thus, an electrostatic filter arrangement typically has a gas supply which is arranged ahead of the electrostatic filter and which guides the gas to be filtered as uniformly as possible towards and into the filter. The gas supply usually includes an incoming flow channel, through which the gas flows in the direction of the filter, and a gas inlet hood, which expands from the incoming flow channel to the electrostatic filter approximately in the shape of an inverted funnel. The gas inlet hood thus has a small cross-sectional area, which corresponds to the incoming flow channel, at its cross section at the front in the direction of flow and a large cross-sectional area, which essentially corresponds to that of the electrostatic filter, at its cross section at the back in the direction of flow.
To make the flow into the filter uniform, at least one flow distributor is arranged in the gas supply, normally directly before the electrostatic filter in the expanded region of the gas inlet hood. These flow distributors are typically gas distribution arrangements in the form of perforated plates, which are often arranged one behind the other in several layers.
For further improvement of the filter performance, or simply to create the initial conditions necessary for filtration in the gas to be filtered, conditioning means are mixed into the gas flow in the gas supply with the aid of an admixture arrangement. One example is cooling conditioning, for which water is sprayed into the gas flow to cool the gas. The gas is also often conditioned without reducing the gas temperature by injecting SO3, NH3, water vapor, or the like into the gas to be filtered, among other things, for reducing the electrical resistance of the dust. To achieve as uniform an admixture as possible, the admixture arrangement usually has a plurality of nozzles arranged in the gas supply.
These known electrostatic filter arrangements have already proven to be very effective in the past. However, against the background of increasingly stricter requirements for emission protection of filtration systems, there is nevertheless still a great demand for electrostatic filter arrangements which exhibit an improved efficiency relative to this state of the art.